1. Field of the Invention
The present invention relates to a catadioptric optical system suitable for magnifying and observing a sample (an object), and an image pickup apparatus having the catadioptric optical system.
2. Description of the Related Art
In a current pathological examination, a pathological sample (a sample) is directly observed by a human eye using an optical microscope. Recently, a so-called virtual microscope in which the pathological sample is obtained as image data to be observed on a display is used. In the virtual microscope, since the image data of the pathological sample can be observed on the display, it can be observed by more than one person at the same time. In addition, using this virtual microscope, there are a lot of advantages that the image data is shared with a distant pathologist to seek the diagnosis or the like. However, there is a problem that this method takes time in order to take an image of the pathological sample to be obtained as image data.
One of reasons that the method takes time is that the pathological sample with a wide image-pickup range needs to be obtained as image data using a narrow image-pickup range of the microscope. When the image-pickup range of the microscope is narrow, taking the image more than once or connecting images while scanning the pathological sample is needed to obtain one image. In order to reduce the time that needs to obtain the image data while decreasing the number of times of taking the image compared to a conventional method, an optical system (an image pickup optical system) with a wide image-pickup range is required.
Additionally, in observing the pathological sample, an optical system that has a high resolution in a visible range (a wide wavelength range) as well as the wide image-pickup range is required. The optical system with a high resolution is required in a variety of fields, as well as the usage of the pathological diagnosis. Japanese Patent Publication No. S60-034737 discloses an objective lens of a microscope that is suitable for observing a living cell or the like in which an aberration is appropriately reduced over an entire range of visible light.
Japanese Translation of PCT Application No. 2007-514179 discloses a ultrawideband-ultraviolet microscope video system that has a high resolution over a wide wavelength range of ultraviolet using a catadioptric optical system in order to examine a defect that exists on an integrated circuit or a photomask. International Publication No. WO00/039623 discloses a catadioptric optical system that is suitable for exposing a fine pattern in a wide range to manufacture a semiconductor device.
There is a catadioptric optical system that is configured by combining a catoptric optical system with a dioptric optical system as an optical system that is suitable for appropriately reducing the aberration over the entire range of visible light. In this catadioptric optical system, using a phenomenon that the effect on Petzval sum for a surface shape is opposite between a reflective surface and a refractive surface, the aberration is appropriately reduced over the entire range of the visible light while a compact optical system is achieved by combining a concave reflection surface and a convex lens that have a light collection function.
In this catadioptric optical system, a wide observation range and a high optical performance over a wide wavelength range are required to observe a magnified sample.
In many catadioptric optical systems, an aperture stop that limits a marginal portion of a light beam in an optical path in the optical system is provided in order to set the numerical aperture of the optical system and set an entrance pupil and an exit pupil. In order to obtain a wide observation field of view, and a wide entire field of view and a high optical performance over the entire field of view in the catadioptric optical system, it is important that a position on an optical axis of the aperture stop that limits the light beam is arranged at an appropriate position. If the position of the aperture stop is inappropriate, it is difficult to appropriately limit a diameter of the light beam that enters an entire screen, and therefore it is difficult to obtain the high optical performance because of the increase of flare.